1. Technical Field
The present invention relates to a rotor blade flap drive apparatus that drives a flap provided at a trailing edge of each rotor blade in a helicopter or the like.
2. Background Art
In recent years, demand has increased for commuter helicopters that take off and land at urban heliports. To realize this operation, noise reduction of helicopters is strongly required. As one effective means for accomplishing such a noise reduction strategy, a technique is contemplated wherein a flap is attached to a helicopter rotor blade and drives those flap at a high speed of approximately 30 Hz to 50 Hz in order to improve aerodynamic characteristics of the rotor blade.
As an apparatus for realizing high-speed driving of a flap in this manner, the present applicant has proposed the rotor blade flap drive apparatus of Japanese Patent Application No. 10-076246 (1998). In order to be housed within the blade, an actuator employed by the flap drive apparatus should be small and lightweight, and in the aforementioned rotor blade flap drive apparatus a piezoelectric actuator is used as the actuator therein. Because piezoelectric actuator displacement is very small, in driving the flap, actuator displacement is magnified by means of a displacement magnification mechanism.
FIG. 16 is a plan view showing one example of such a conventional rotor blade flap drive apparatus 1, and FIG. 17 is a side view thereof. In the rotor blade flap drive apparatus 1, an eccentric shaft 3 is employed as a displacement magnification mechanism 2. Eccentric shaft 3 possesses a first shaft 12 and a second shaft 13 having mutually eccentric axes 10, 1, and a bearing 4 which supports the first shaft 12 is fixed relative to the blade. Output portions 6a, 7a of two actuators 6, 7 are coupled by way of a coupling member 14 to a bearing 5 which supports the second shaft 13. Fixed to this eccentric shaft 3 is a swing arm 8, and a connecting rod 9, which is, coupled to the tip of this swing arm 8, is connected to-the flap.
Simultaneous extension/contraction of the two actuators 6, 7 causes reciprocating angular displacement of the eccentric shaft 3 about the axis 10 of the first shaft 12, which is supported fixedly relative to the blade, resulting in large lead-lag swing of the swing arm 8 which is fixed to this eccentric shaft 3. Swing of the swing arm 8, which is thus made to swing-in a lead and lag direction with large amplitude, is transmitted by way of the connecting rod 9 to the flap, resulting in the flap motion in vertical reciprocating angular displacement fashion.
In order to obtain a large driving force with such a flap drive apparatus 1, the two actuators 6, 7 are employed, as has been described above, and the respective actuators 6, 7 are driven in synchronous fashion. The output portions 6a, 7a of the two actuators 6, 7 are fixed together in an integral fashion by the coupling member 14, and are coupled to the bearing 4 for the second shaft 13 of the eccentric shaft 3. Accordingly, while there is no Ads problem when the two actuators 6, 7 are displaced in proper synchronous fashion, even a slight disagreement in synchronization will result in slight distortion at the periphery of the eccentric shaft 3, causing a large reduction in the displacement magnification factor and resulting in swing instability. Furthermore, it is extremely difficult to control the actuators 6, 7, which are displaced at high speed, such that they are synchronized with high precision.
The object of the present invention is to provide a rotor blade flap drive apparatus having a simple construction and being capable of causing stable swing of a swing arm in a displacement magnification mechanism.
The invention provides a rotor blade flap drive apparatus comprising: a flap attached to a trailing edge of a blade so as to permit vertical angular displacement, and a pair of actuators housed within the blade and having output portions which are displaced in mutually reverse phases. A swing arm has a base portion which forms a side end of the actuator and is coupled to the respective output portions of the pair of actuators so as to be angularly disposed, and has a tip that swings in a lead and lag direction, and which is at a side opposite to the base portion. A connecting rod connects the tip of the swing arm and the flap.
In accordance with the present invention, the two actuators have output portions that are displaced in mutually reverse phase. That is, when one of the actuators is extended the other actuator contracts, and conversely, when one of the actuators contracts the other actuator is extended.
Accordingly, the tip of the swing arm, the base portion of which is coupled to the output portions of two such actuators, will as a result hereof swing in a lead and lag. direction with large amplitude, and the swing of the swing arm will, by way of the connecting rod, cause vertical reciprocating angular displacement of the flap.
With the above-described conventional flap drive apparatus, the two actuators are extended/contracted simultaneously in synchronous fashion and the output portions are fixedly coupled. Therefore, even a slight disagreement in synchronization causes the swing arm to no longer swing smoothly but rather to become unstable. In contrast, in the present invention swing is made to occur such that the output portions of the two actuators are displaced so as to be mutually reverse in phase. Therefore, the swing arm swings about an imaginary central swing axis located centrally between respective output portions. Accordingly, even when the phases of the two actuators are not exactly reverse but are in slight disagreement, the location of the imaginary central axis of swing of the swing arm will simply be displaced slightly and there will be no reduction in displacement magnification factor, permitting automatic adjustment of swing. The swing arm can thus be made to swing stably through employment of a simple structure.
Furthermore, in the conventional method, the angle of the swing arm would be changed in the event that a large centrifugal force caused application of a compressive force on the actuator and slight contraction of the actuator. However, the present invention has the advantage that because the angle of the swing arm will remain unchanged, there is no need to take into account the effect of the magnitude of the centrifugal force on the angle of the swing arm.
Moreover, because in the invention the swing arm is made to swing through use of the difference in phase between the output portions of two actuators (as compared with the conventional structure wherein actuators are simultaneously extended/contracted in synchronous fashion), it is possible to achieve output displacement magnification relative to actuator displacement that are approximately two times those of flap drive apparatuses having conventional structures.
In the invention it is preferable that the apparatus comprises an eccentric shaft in which a first shaft and a second shaft have axes that are mutually parallel and are mutually eccentric in a direction perpendicular to the axial direction, and the shafts are connected end-to-end in the axial direction to form an integral structure. A first support supports the first shaft so as to permit angular displacement, and the first support is coupled to the output portion of a first one of the actuators. A second support supports the second shaft so as to permit angular displacement, and the second support is coupled to the output portion of the second one of the actuators. The swing arm is fixed to a periphery of the eccentric shaft perpendicularly with respect to the eccentric shaft.
In accordance with the present invention, actuator displacement is magnified by the eccentric shaft and the swing arm which is fixed to the eccentric shaft. Because the magnification factor is determined by the ratio between the amount of eccentricity and the length of the swing arm, the amount of eccentricity must be made small in order to reduce the size of construction and increase the size of the magnification factor. Furthermore, the first shaft and the second shaft, as well as the first bearing and the second bearing which support these, must inevitably be made large for stable driving of the swing arm. Arranging the first and second shafts in parallel would also make it unavoidable for the amount of eccentricity to be made large. However, the invention permits the amount of eccentricity to be made as small as possible and the magnification factor to be made as large as possible as a result of the fact that the first shaft and the second shaft are connected end-to-end in the axial direction to form an integral structure. Furthermore, this also makes it possible for the first bearing and the second bearing, which support the respective shafts, to be arranged such that they are offset in the axial direction, permitting stable support.
Furthermore, in the invention it is preferable that the swing arm comprises a tip that swings in a lead and lag direction, and a base portion having two axes extending vertically and arranged such that they are spaced apart in the lead-lag direction. The output portion of a first one of the actuators is coupled to one of the lead-wise and lag-wise base portion axes so as to permit angular displacement, and the output portion of the second one of the actuators is coupled to the other of the lead-wise and lag-wise base portion axes so as to permit angular displacement.
In accordance with the invention, respective output shafts of the two actuators arranged in the lead and lag direction are coupled to the base portion of the swing arm so as to permit angular displacement. Accordingly, displacing the respective output shafts in opposite directions such that they are reverse in phase causes the tip of the swing arm to swing in a lead and lag direction with a large amplitude, and causes the flap to be driven vertically in a reciprocating angular displacement fashion by way of the connecting rod which is connected to the tip. The swing arm can thus be driven stably through employment of such a simple construction.
In the invention, it is further preferable that the swing arm comprises a pair of links, with a base portion of a first one of the links being coupled to the output portion of a first one of the actuators so as to permit angular displacement, and a base portion of the second one of the links being coupled to the output portion of the second one of the actuators so as to permit angular displacement. A tip of the first one of the links and a tip of the second one of the links are coupled so as to permit angular displacement, and the connecting rod is connected to these tips.
In accordance with the present invention, the swing arm is constructed in a so-called toggle-link fashion, which is to say that base portions of respective links are coupled to the output portions of the respective actuators so as to permit angular displacement, and-the tips are coupled to each other. With such a toggle-link-type swing arm as well, displacing respective actuator output portions in reverse phase causes the tip to swing in a lead and lag direction with a large amplitude, and causes the flap to be driven vertically in a reciprocating angular displacement fashion by way of the connecting rod which is connected to the tip. In this way, the output portions displaced in reverse phase and the toggle-link-type swing arm permits stable swinging drive of a swing arm.
Moreover, in the invention it is preferable that the apparatus comprises linear guide means mounted within the blade so as to allow the output portion of one of the actuators to undergo displacement only along a-displacement direction of the actuator thereof but preventing the output portion from undergoing displacement in a direction perpendicular to the displacement direction of the actuator.
In accordance with the present invention, because the output portion of one of the actuators undergoes displacement properly in a linear direction through the use of a linear guide means, the reactive force of the flap which acts by way of the connecting rod is generated by the linear guide means, permitting the swing arm to be driven stably and properly. Because the construction is such that the swing arm is made to swing as a result of causing the respective output portions which are coupled to the base portions of the swing arm to provide linear displacement so as to be more or less mutually parallel and reverse in phase, the paths of motion of the respective output portions are not perfectly parallel lines but paths of motion that bulge slightly in the central region in the displacement direction. Accordingly, by providing linear guide means at the output portion of only one of the actuators and not at the other, a slight difference in path of motion is allowed, permitting the swing arm to be driven stably and properly.
Furthermore, in the invention it is preferable that the apparatus comprises a spring member intervening between the swing arm and the blade. This causes action, when the swing arm is angularly displaced to either side of a neutral position thereof, of a spring force in such a direction to encourage such angular displacement.
In accordance with the invention, when the swing arm is angularly displaced to either side past its neutral position, a spring force from the spring member causes encouragement of that angular displacement, and rapid angular displacement to the full-stroke position on that side is obtained. Conversely, when the swing arm is angularly displaced from this side to the other side, past the neutral position, angular displacement to the other side is encouraged. Accordingly, by causing a lead-lag swing of the swing arm centered on its neutral position through the use of the actuators, it is possible to enable the swing arm to undergo reliable, rapid reciprocating angular displacement through its full stroke. It is thus possible to improve response through employment of such a simple construction.
Furthermore, this spring force acts so as to cancel the hinge moment acting on the flap and so as to assist driving of the flap by the actuators.
Moreover, in the invention it is preferable that the apparatus comprises a spring member intervening between the flap and the blade, for causing action, when the flap is angularly displaced to either side of a neutral position thereof, of a spring force in such a direction to encourage such angular displacement.
In accordance with the invention, the flap is equipped with a spring member in the same manner as the foregoing, and this spring member is arranged such that when the flap is angularly displaced upwardly past its neutral position, the spring member encourages the angular displacement and causes angular displacement to the upward limiting position. Conversely, when the flap is angularly displaced downwardly past its neutral position, the spring member causes driving of the angular displacement to the downward limiting position. Response can thus be improved through employment of a simple construction.
Furthermore, like the above-described spring provided at the swing arm, this spring is also such that the spring force therefrom causes cancellation of the hinge moment acting on the flap and acts so as to assist the actuators.
Furthermore, in the invention it is preferable that the apparatus comprises a spring actuator intervening between the spring member and the blade, for applying variation of the spring force from the spring member.
The hinge moment acting on the flap varies cyclically with blade rotation and so forth. A spring actuator is provided at the spring member attached to the swing arm or the flap, permitting spring force to be varied by means of this actuator. Accordingly, by using the spring actuator to vary spring force corresponding to the hinge moment acting on the flap, it is possible to assist actuator movement with optimum force.
Furthermore, in the invention it is preferable that the apparatus comprises an input shaft parallel to the axis of the flap angular displacement shaft and fixed to the flap angular displacement shaft eccentrically in a vertical direction. A rod end supports the input shaft so as to permit angular displacement, and connects the connecting rod thereto perpendicularly with respect to the axis of the input shaft.
In accordance with the present invention, input of a displacement from the connecting rod, which undergoes displacement lead and lag direction, to the input shaft, which is fixed eccentrically to the flap angular displacement shaft, causes the displacement of the connecting rod to be magnified, the input arm length being the amount of eccentricity, and causes the flap to undergo angular displacement with a large amplitude. The flap can thus be made to stably undergo magnified displacement through employment of the eccentric input shaft and the rod end which supports the input shaft.
Moreover, in the invention it is preferable that the actuators comprise stack-type piezoelectric actuators in which a plurality of piezoelectric element sheets that undergo displacement in correspondence to a voltage applied thereto are laminated. The sheets are arranged such that a displacement direction thereof is in a blade spanwise direction, and the ends of the actuators at the blade tip side are fixed to the blade.
It is necessary to apply a preload to a stack-type piezoelectric actuator such that it is compressed in the displacement direction during operation. In the invention, however, the actuators are arranged so as to lie along the blade spanwise direction, and the ends of the actuators at the blade tip side are furthermore fixed to the blade. Therefore, the centrifugal force produced during rotation of the rotor blade causes application of a preload on the actuators. As a result, the need to use a spring or the like to apply a preload is eliminated, permitting reduction in the number of components and simplification of the construction.
Furthermore, in the invention it is preferable that the actuators comprise giant magnetostrictive actuators that are displaced as a result of a change in a magnetic field produced by an electric current through an electromagnetic coil. The actuators are arranged such that the displacement direction is in a blade spanwise direction, and one end of each of the actuators at the blade tip side is fixed to the blade.
While it is also necessary to apply a preload to a giant magnetostrictive actuator in the displacement direction, because the actuators are arranged so as to lie along the spanwise direction and because the ends of the actuators at the blade tip side are fixed to the blade, the centrifugal force produced during rotation of the rotor blade causes application of a preload on the actuators. As a result, the need to use a spring or the like to apply a preload is eliminated, permitting reduction in the number of components and simplification of the construction.